Biomedical Engineering Reference
In-Depth Information
gene therapy trials worldwide, either completed, enrolling patients,
or waiting for permission to proceed from the National Institutes
of Health Human Gene Therapy Subcommittee. Although most
gene therapy trials now focus on treating cancer, the earliest stud-
ies of gene therapy were designed to treat inherited diseases such as
cystic fibrosis and immune deficiency disorders. As scientists pin-
pointed the specific miscoded genes for inherited diseases and
learned to change the genetic coding of cells in the laboratory, they
thought it would be both possible and useful to insert a correct
gene into the genome of the cells affected by the disorder. If the
process worked with cells in the laboratory, then getting it to work
in the body would not be so difficult, but only if the cells affected
by the inherited defect were easily reached. For example, in the
most common form of dwarfism, the inherited defect occurs in a
gene that provides a docking protein for a growth factor that is
responsible for the development of bones in fetuses and children.
It would be very difficult to replace the docking protein everywhere
in the body. In contrast, Ashanti's immunodeficiency is the result
of something missing in the formation of her immune system
cells. Researchers knew that the condition could be treated with
a transplant of bone marrow cells from a suitable donor, so they
needed to target only the bone marrow, and they had learned how
to do that from over 30 years of using bone marrow transplants to
treat leukemia and other blood disorders. The sequencing of the
human genome, completed in late 2003, may still open up many
more targets for gene therapy.
The challenge is to get the genetic construct into the appropri-
ate cell, and have it settle down in the cell to be copied faithfully
every time the cell divides. Most importantly, it must be placed
where it would direct the production of the correct protein so that
the protein would be produced in the right amount and in the
proper location within the cell. So far, gene therapy has not had
much success.
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